The Sun Rx

The more SPF the better, right? Maybe not. Turns out some 'screen-free time outdoors may be just what the doctor ordered.

Text by Kate Rope

Illustration by Heads of State

Just three miles into the Olympic marathon in Beijing last summer, American record-holder Deena Kastor, 36, felt a pop in her right foot and dropped to the ground in pain from a broken metatarsal. The cause: A deficiency in vitamin D had weakened her bones.

Three out of four Americans today aren’t getting enough vitamin D, and the ramifications could be severe. A deficit has been linked to everything from cancer to diabetes, osteoporosis, and heart disease. Numerous studies have shown the benefits of D: It aids calcium absorption, keeps us agile as we age, and may fend off colds. It could even make us better athletes, improving reaction time and building muscles.